Good looking sandy haired, dreamy... those are some of the descriptions Arthur Laurents gives Tony. But that's the problem, he may be good looking and dreamy but he's also supposed to be the co-founder of the Jets; which is a job that requires a lot more than good looks. Tony has to be a tough guy, the equal or better of Riff and yet more often than not he's simply portrayed as the good looking dreamy fellow. Someone with a "rep that's bigger than the whole West Side" should project the grit and toughness required to be a famous brawler, not just be tall and broad shouldered.
Look what happens at the rumble. Riff is stabbed by Bernardo, he turns towards Tony and reaches out with his knife arm, Tony grasps Riff and lowers him to the ground and then crouches on the ground next to him. So what is he doing down there? Clearly, he's watching the light go out of Riff's eyes and the blood pool around him so that when it's clear the Riff is gone what's the first thing Tony does. He leaps to his feet, knife in hand and goes after the person who killed Riff. I think it's very clear that at that point in time he doesn't even remember that that person is Maria's brother, his whole being is focused on one thing - destroy the person who destroyed his best friend - his surrogate brother. Certainly the Jets in the ensuing scenes don't seem to see anything odd about Tony's behavior, they recognize that he's still worthy of that rep and that's why they are willing to protect him from Chino.
And that's why Tony is such a tricky role to play, you have to be both lover and killer; and the audience has to believe that you are capable of both.